Thirteen years ago, on a balmy South African evening in September, an eclectic group of guests arrived in Pretoria for a dinner with Nelson Mandela. Despite the somewhat incongruous presence of a former warlord, they ate, drank and made merry. The host wore one of his trademark shirts, and in the morning one of the guests woke up with some diamonds.

So much, and very little more, is known for certain about the night of 25 September 1997, when Naomi Campbell says she was given some "dirty-looking stones" by mysterious men who showed up – allegedly at the behest of Charles Taylor, the former Liberian leader – at her bedroom door in the middle of the night.

Today, the testimony of two witnesses was supposed to shine a light on this exchange, which prosecutors in The Hague believe could be a crucial link between the former warlord and the trade in conflict gems. They ended up doing more to confuse than illuminate.

Taking the stand in the special court for Sierra Leone, Campbell's former modelling agent Carole White recounted a version of events that tore to pieces the account given by the model last week. Campbell and Taylor, she said, had been "mildly flirting" at the dinner. At a certain point in the evening, she alleged, he had told her he would give her some diamonds.

In her testimony last week, Campbell insisted she had not known the diamonds were coming, and the possibility that Taylor was the mysterious donor had only occurred to her the next morning.

"We were talking about Africa, I think, whilst we were eating," said White. "Naomi leant back and Charles Taylor leaned forward; Naomi Campbell was very excited and she told me: 'He's going to give me some diamonds.'"

At the end of the dinner, she continued, Taylor and a man White identified as Liberia's then defence minister discussed with her and Campbell how they were going to get the gift to the Mandelas' residence.

They said they would have to go to Johannesburg to pick them up, she alleged. "The diamonds were to be brought to the guesthouse where Naomi Campbell was staying," she said.

Prosecutors argue that, while in South Africa, Taylor sold on a batch of "blood diamonds" he had been given by rebels in Sierra Leone. He vehemently denies this, along with all 11 counts of war crimes and crimes against humanity that have been put to him by the court.

According to White, she and Campbell waited as night fell for the diamonds to arrive. Campbell, she said, was very excited and communicating with someone by mobile phone. Eventually, after the two had decided to go to bed, she said, she heard a noise at her window.

"I looked down and there were two guys on the ground. They said, we have something for Ms Campbell," said White. Campbell, in her nightdress and a cashmere shawl, welcomed the men inside and gave them Coca-Cola, she added. The diamonds were unwrapped, and Campbell was "quite disappointed", she said, "because they weren't shiny" but dirty and small.

The account differs significantly from the model's 90-minute testimony under subpoena last week. She denied having spoken with Taylor, said she had never heard of Liberia, and told the court it was Mia Farrow, who was also staying at the presidential guesthouse, who put the idea that the diamonds were from Taylor into her head over breakfast.

That part of her testimony, too, was countered today as Farrow told the court that Campbell's claims to have been unaware of the gift's origin were untrue. Asked whether, as the model had said, it was Farrow herself who had suggested the gift had come from Taylor, Farrow replied: "Absolutely not. Naomi Campbell said they came from Charles Taylor."

Speaking softly, she added: "What I remember is Naomi Campbell joined us at the [breakfast] table, but before she even sat down she recounted an event of that evening.

"She said that in the night she had been awakened and some men were knocking at the door and they had been sent by Charles Taylor and … they had given her a huge diamond. And she said she intended to give the diamonds to Nelson Mandela's children's fund."

However, if the prosecution had hoped that the testimony of these two witnesses would give extra weight to the alleged link between Taylor and "blood diamonds", they had not reckoned with the agility of Courtenay Griffiths, defence lawyer for the alleged war criminal.

According to him and another defence lawyer, Morris Anyah, Farrow and White were not impartial witnesses but women with agendas. Farrow, argued Anyah, was basing her allegations on a patchy memory of an event that took place 13 years ago.

Under cross-examination, she admitted she could remember neither where she was sitting at the dinner nor whether Taylor had stayed to eat. She had problems remembering her son's age – "maths isn't my forte" – and described Imran Khan, the Pakistani cricketer and fellow guest, as a "soccer player".

At one stage, the chief judge even asked her if her memory had been clouded by the 2006 film Blood Diamond starring Leonardo DiCaprio.

But, in a more serious accusation, the defence said Farrow, a Unicef goodwill ambassador who last year went on hunger strike over the expulsion of aid agencies from Darfur, was prevented from objectivity by highly emotional devotion to Africa. They cited her editing of a Guardian article that she put on her blog, with slight amendments, as proof that she was irrevocably set against the accused.

"My view is that it is quite clear that Mia Farrow is here to follow her own agenda. She sees herself as the modern day Mother Theresa of Africa," said Griffiths in a press conference.

It was in his cross-examination of White, however, that Griffiths reached his peak. He accused White of trying to smear Campbell by linking her with Taylor. The agent, whom Campbell once described as her surrogate mother, has launched a lawsuit for breach of contract against Campbell, from which she stands to win, according to Griffiths, millions. Her testimony was, he claimed, compromised by her desire to make Campbell look bad.

"You come with an agenda," he told her. "And I suggest that your motive for lying about Naomi Campbell is to provide yourself with ammunition against her in the [breach of contract] lawsuit."

"That's not true," responded White, scowling into the artificial light of the courtroom.

Who says what?

Naomi Campbell

Where did Naomi sit at the dinner: Between Nelson Mandela and Quincy Jones

How many diamonds: Two or three dirty looking stones

Link between Charles Taylor and stones: Either Farrow or White mentioned over breakfast

Circumstances of delivery: Two unidentified men came to door with a pouch of gems

Why she gave them away: She was uncomfortable taking gifts while working for charity

Mia Farrow

Where did Naomi sit at the dinner: I don't remember

How many diamonds: One huge gem

Link between CharlesTaylor and stones: Campbell announced it over breakfast

Circumstances of delivery: Men presenting themselves as working for Charles Taylor came to the door

Why she gave them away: She thought it improper to keep them and had decided by the following morning

Carole White

Where did Naomi sit at the dinner: Between Charles Taylor and his "minister of defence"

How many diamonds: Five or six

Link between Charles Taylor and stones: Taylor told Campbell over dinner he would bring her diamonds

Circumstances of delivery: Two unidentified men threw stones at White's window and then went in to drink Coca-Cola with Campbell and White

Why she gave them away: She was eventually persuaded later the following day that it would be illegal to take them out of South Africa

Diamond night

The court was shown pictures of what was described as a "blood diamond party" held by Carole White's employees on Thursday, the day of Naomi Campbell's testimony. Charles Taylor's defence lawyer, Courtenay Griffiths QC, showed a series of pictures posted on Facebook and tagged "blood diamond night" by one of White's booking agents, Annie Wilshaw. White, who appeared in the pictures, said the party was simply an event to mark the opening of the agency's new house for models. In comments made under the photographs, White's staff made clear their attitude to Naomi Campbell's testimony that day. Referring to the model's testimony that her appearance was a "big inconvenience", Wilshaw wrote on her wall: "this is a big inconvenience .... it will be when carole arrives at the hague & ruins your tale on monday." "I have the diamonds…." wrote back Ridout. "Kidney stones" replied Wilshaw. By this evening, some of the comments had been modified.